If you'd like to change the logo placed in the email footer and the end of the Campaign, you can do so by:
Navigate to Admin > Account Settings
Scroll to Footer Logo URL
Click on the "Select an image" section
Use an image from the media library or upload a new image into the media library and choose the image
Save
Note
Existing communication emails will not be updated if previously different
This is an add-on feature, if you'd like this feature enabled please speak with your Account Manager